AVS 52nd International Symposium
    Applied Surface Science Monday Sessions
       Session AS+BI+NS-MoM

Paper AS+BI+NS-MoM8
Surface Potential Mapping of DNA-protein Complex at Molecular Level

Monday, October 31, 2005, 10:40 am, Room 206

Session: Nanoscale Analysis: Biomaterial and Other Applications
Presenter: E. Mikamo, Osaka University, Japan
Authors: E. Mikamo, Osaka University, Japan
F. Yamada, Osaka University, Japan
T. Matsumoto, Osaka University, Japan
T. Kawai, Osaka University, Japan
Correspondent: Click to Email
Atomic force microscopy (AFM) is a valuable method for the study of biomolecules such as DNA, RNA and proteins at real-space. The biomolecules have generally been adsorbed on the insulating substrate as mica to observe by AFM. However, it is very hard to measure the local electric properties of the insulating substrate and the conductive substrate has been commonly used. Recently our group demonstrated the measurement of electric properties of DNA and Au nanoparticles on mica and sapphire substrate. This result encouraged us to measure the complex of biomolecules on the insulating substrate at molecular level. We report here surface potential and capacitance measurement of DNA, protein and DNA-protein complex on the insulating substrate. The experiments are based on frequency mode non-contact AFM (FM-ncAFM). The FM-ncAFM is able to detect the high-sensitive local electrostatic forces and prevent the charge injection caused by tip-sample contact. We observed the surface potential mapping and topographic image simultaneously. The topographic images clearly showed DNA and protein as line and dot structure. The surface potential of corresponded structures is observed as bright contrast. Our results indicate that surface potential of DNA, protein and DNA-protein complex is higher than insulating substrate surface. The potential images resolve the double strand DNA, thin structure less than 2 nm, and protein at single molecular revel. To estimate the capacitance of individual molecules, we measured d(@DELTA@F) per dV images. The measurement of surface potential and capacitance indicate that this technique is able to discriminate the individual molecules on an insulating substrate. This work was supported by grants from the New Energy and Industrial Technology Development Organization (NEDO).